This invention relates generally to a hydraulic accumulator-compressor, and more particularly to a hydraulic accumulator-compressor in geothermal power control systems having as an objective producing engineered fluids for enhanced oil recovery from geopressured geothermal power and enhanced natural gas recovery from the well fluid.
Economic production of oil from an underground formation becomes impossible when the reservoir pressure drops below a certain level. When that occurs it has become the practice to employ one or more methods of secondary and tertiary oil recovery. These methods try to provide a new driving force to displace oil from rock formations toward adjacent production wells in the same field. The techniques have centered upon engineered floods of natural gas, CO.sub.2, water, and polymer aqeous solutions for the purpose of (1) physically changing the properties of oil (density, viscosity, surface tension and wetting characteristics), and (2) in uniformly sweeping it through the reservoir.
Compared with water flooding, miscible flooding is the more sophisticated technique for oil displacement. The oil is diluted with natural gas, CO.sub.2 or other light hydrocarbons in order to reduce viscosity and increase mobility of the oil. The more expensive miscible flooding is usually followed by a mixture of water and surfactant (detergent, ammonia, etc.). A diffusion front (oil saturation bank) is caused by the first miscible flooding and formed near the injection well. Remaining oil droplets are mobilized by the surfactant and water to complete the oil bank that sweeps the remaining reservoir oil through the rock to production wells. At the end polymerized water (micellar polymer), with high viscosity and the ability to maintain a stable and uniform flood front, is pumped into the injection well as a sweep or displacement mechanism. Performance of the system will increase when all fluids are heated because the miscible phase is more soluble, the fluid viscosities are reduced, and the surfactant has better cleaning or wetting properties.
Instead of pumping the fluids to displace oil from reservoir rocks, it is more economic to use the hydraulic energy available in a geopressured aquifer. These concepts have centered upon using hot brine as a motive force behind the engineered fluids. Geopressured wells of commercial productivity (i.e., 10-40,000 BPD for ten years) are not likely to be found at the same level as productive oil and gas wells. These levels are usually highly faulted producing small structural traps. In productive areas, wells are often drilled to great depths in search of oil and gas only to locate water saturated sands. That happens more often than not. But during the life of the productive field, one can expect a deeper test well, and it will almost certainly reveal some geopressured brine zone that has more than enough fluid under pressure to sweep an existing pressure depleted oil field.
In most cases, artificial floods are composed of engineered fluids of specified compositions and injected at controlled rates. The objective of such flooding is to design a general process for enhanced oil recovery utilizing the hydraulic and thermal energy of geopressured geothermal brine resources as a means for offsetting the cost of the water flood. The invention described in U.S. Pat. No. 4,484,446 by the present inventor was made in satisfaction of that objective.
Another objective of the exploitation of geopressured geothermal energy resource fluids is an outgrowth of the shortage of natural gas in recent years. Brine is typically saturated with natural gas in quantities of from thirty to fifty standard cubic feet per barrel (5.34-8.91 m.sup.3 gas/m.sup.3 (brine) at 250.degree. F. to 450.degree. F. (395 K to 505 K). The large extent of that resource has prompted various estimates of recoverable gas reserves that could extend the U.S. reserve life index as much as two hundred years. The present invention addresses the need to recover the natural gas as well as the production of engineered fluids.